1. Field of the Invention
This present invention relates to the field of pipeline inspection and testing, and more specifically to the field of pipeline inspection using electronic testing apparatus.
2. Discussion of the Prior Art
It is sometimes necessary to periodically inspect gas, oil, water and other metal pipelines for cracks, weakened spots, wall thinning, and other abnormalities caused by wear, trauma and/or corrosion. These typically are inspected using currently known electronic testing techniques, such as a magnetic flux leakage technique. The magnetic flux leakage technique is more fully explained in “Intelligent Pig Inspection of Uncoated Seamless Pipelines” by Terry R. Shamblin, Columbia Gas Transmission, Charleston, W. Va. in the March 200 issue of Pipeline and Gas Journal, and in “Research on Intelligent Pipeline Flux Leakage Detector” by Yang-Lijian and Wong-Yumei from the School of Information Science and Engineering, Shenyang Univ. Of Technology, Shenyang, China, hereby incorporated by reference as if set forth in their entirety herein. In this technique, conductive brushes each having a conductive base mounted around the perimeter of a hub, are rotated as they are passed through the inside of a pipeline. A magnetic source passes magnetic flux through the hub, through the base of the brushes and through the bristles. The bristles are brushed against the inner walls of the pipeline, thereby passing magnetic flux into the metal pipeline walls.
A magnetic flux measuring device having a number of magnetic sensors, follows closely behind the inspection brush on or near the pipeline inner surface and reads the remaining magnetic flux. The difference in the magnetic flux induced by the brushes and the readings from the magnetic sensors results in a measure of magnetic flux leakage for each location inside of the pipe. The magnetic flux leakage is related to pipe thinning, pipe weakening, pipe corrosion and other abnormalities. The magnetic flux leakage test therefore is an efficient test for abnormalities of a metal pipeline.
The inspection brush is comprised of a plurality of elongated pencil end brushes, having conductive metal bristles extending from a base cup. These prior art pencil end brushes are typically constructed having metal bristles, usually steel, that are soldered into a base cup. The base cup is connected to a magnetic source and is designed to pass magnetic flux from the magnetic source, to the bristles, then from the bristles to the pipeline walls.
There are known prior art methods of constructing these pencil brushes. These include cutting the bristles to a specified length, inserting them into a cup and attaching to the cup with an attaching medium such as solder or epoxy. The open edge of the cup may or may not be crimped where the bristles enter the cup.
The prior art attachment methods are subject to failure where the bristles are not fully embedded in the attaching medium. Brush integrity requires that every bristle be fully in contact with the attaching medium. Partial contact with the medium results in reduced strength of the brush. It is difficult, if not impossible to assure that each bristle is in full contact and the only method of being certain of that is by a destructive disassembly of the brush.
During use of the inspection brush inside of the pipeline, bristles may be pulled out of or otherwise fall out of the brush or the entire brush may fall apart. The pieces will be dispersed throughout the system. This would cause great damage to the pipeline pumps, valves, seals and related equipment. It would also be a very costly and time consuming process to ‘fish’ all of the pieces.
Since nickel is a good electrical conductor and conducts magnetic flux very well, nickel plated bristles are preferred. The use of nickel plating would allow the testing process to be performed much more quickly and efficiently indirectly saving large amounts of money in ‘down time’ since the pipeline may not be used during the testing process. However, the attachment of nickel plated parts is not easily attached using solder or epoxy. This again results in reduced strength of the brush.
Another goal of the brush is to maximize electrical conductivity from the base housing to the bristles to the pipeline wall. Firm contact must be maintained between the base housing and the bristles to maintain high magnetic flux. Bristles that are held partially by solder or epoxy will have reduced contact and therefore reducing conductivity.
An alternate means of securing nickel plated bristles would be to position the bristles inside the base housing, then compress the upper edge of the base housing to crimp the bristles in place. This crimping alone results in a weakened brush with low electrical conductivity.
Therefore, there currently is a need for a high magnetic testing brush which is very resilient and would not release bristles into the pipeline.